Fix spaces to tabs

Revert "Fix spaces to tabs"

This reverts commit 3e537d09ef3d3f11b485e7f1695ecdcc14cc08c1.
Add a simple 404, when there is no routing rule.
Improve building the docs and the docs middleware.

- Store the path and filename in the docs toc JSON
- Read the HTML files upfront, cache them, no chance of shady url variables
  passing in fs.reapromiseWithdFile()
- Remove those ugly ~indexOf things.. Don't want to think about it.
fix sidebar missing links
Review improvement suggestions
Make sure the main header is shown on each 404 page.
Fix error where the intro file was not found, simply saving it twice...
Merge pull request #139 from arian/fix-120-404-pages

Fix #120 - Add 404 pages